The present invention relates to the magnetic resonance imaging arts. It finds particular application in conjunction with medical magnetic resonance imaging systems and will be described with particular reference thereto. It is to be appreciated, however, that the present invention may also find application in conjunction with other types of magnetic resonance imaging systems, magnetic resonance spectroscopy systems, and the like.
In magnetic resonance imaging, a substantially uniform main magnetic field is generated within an examination region. The main magnetic field polarizes the nuclear spin system of a subject being imaged within the examination region. Magnetic resonance is excited in dipoles which align with the main magnetic field by transmitting radio frequency excitation signals into the examination region. Specifically, radio frequency pulses transmitted via a radio frequency coil assembly tip the dipoles out of alignment with the main magnetic field and cause a macroscopic magnetic moment vector to precess around an axis parallel to the main magnetic field. The precessing magnetic moment, in turn, generates a corresponding radio frequency magnetic signal as it relaxes and returns to its former state of alignment with the main magnetic field. The radio frequency magnetic resonance signal is received by the radio frequency coil assembly, and from the received signals, an image representation is reconstructed for display on a human viewable display.
In certain medical MRI applications, it is advantageous to perform imaging scans over a limited field of view and depth of penetration of specific regions of the patient being examined. Such regions may include the anus, the prostrate, the cervix, and other regions associated with internal cavities of a patient. RF receive coils of the intracavitary or endocavitary type are generally used to image these regions as the proximity of the coils in such applications provides improved signal-to-noise ratio over a limited field of view and depth of penetration.
Previously, intracavitary or endocavitary RF receive coils made use of an active RP coil element contained within an inflatable non-permeable balloon. An electrical cable interfaced the active RF coil to external electrical circuitry that was used to interface the coil with the magnetic resonance imaging system. The device would be inserted into a cavity associated with the region of interest, for example a patients rectum, and the balloon would then be inflated. Finally, the external electrical interface would be used to tune and match the coil to the MRI system. Typically, such endocavitary coils were disposable and would not be reused for multiple scans. Additionally, the active RF coil element was not rigidly formed, and as such, each individual probe had to be tuned and matched. Another previous form of an endocavitary probe was reusable for a limited number of times before disposal. This form employed additional latex sheathing which could be disposed of between patient uses. However, the device was reused for only a limited number of times.
The previous endocavity RF coil probes employed external tuning and matching circuitry as part of the interface with the MRI system. The electronic tuning procedures were performed for each individual patient the coil was use on. As the active RF coil element was not fixed in location within the probe and could not be repeatedly fixed in position relative to the anatomy being imaged, image performance was not repeatable.
The present invention contemplates a new and improved endocavity RP coil assembly for an MRI apparatus which overcomes the above referenced disadvantages and others.